Monday, October 22, 2012

The Establishment of 'Air House' Standard in Tropical Countries : Part 7

Performance Comparison of Theoretical Model (TM) and PHP 2000

Indoor Air Temperature

Referring to Table 28, the mean temperatures for both cases in TM are slightly higher than PHP 2000 by 0.3 0C. Moreover, the maximum temperatures in TM are higher than PHP 2000 with a difference of 3.7 0C, and the minimum air temperature in TM and PHP 2000 differ by 1.8 0C.

Fondriest Environmental (2012) suggests that when gas molecules move quickly, air temperature will increase and affect other weather parameters such as the rate of evaporation, relative humidity, wind speed and direction. The indoor air temperature is proportional to outside air temperature; therefore, large external openings and louvers that allow air movement into internal spaces contribute to the high temperatures in TM, especially during the day. However, these large openings help to decrease the temperature in TM significantly at night, as suggested by Saini (1970). The best level of temperature is 25.5 0C to 28.0 0C (Hassan & Ramli, 2010). Therefore, the mean and minimum air temperatures in TM are categorized as preferred temperatures.

Relative Humidity

Table 29 displays the results on relative humidity in PHP 2000 and TM. The mean relative humidity in the kitchen area for both cases in TM is slightly lower than that in PHP 2000. The maximum relative humidity results in TM’s cases are 4.8% higher than the PHP 2000 cases. Meanwhile, for minimum relative humidity, the cases in PHP 2000 recorded higher humidity than TM’s cases.

The difference in minimum relative humidity for TM and PHP 2000 is 14.7%. The recommended level of indoor humidity in Malaysia is in the range of 30% to 60%; thus, only results for minimum temperature in all cases are within the recommended level.

The high humidity can only affect the comfort level in a room where the air movement is too low (Saini, 1970). Therefore, the crucial variable that contributes to a good thermal comfort in a building in a tropical climate is air movement.

Internal and External Ventilation

Table 30 shows the internal ventilation results in PHP 2000 and TM. The mean internal ventilation for cases in TM showed an increase compared to cases in PHP 2000, except the kitchen area in case 5. However, there was a significant increase in TM cases for maximum internal ventilation, which ranges from 720.3 l/s to 1273.7 l/s, compared to just 293.2 l/s to 413.3 l/s in PHP 2000.

As has been suggested by Hassan and Ramli (2010), the Beaufort scale has set the best levels of performance for the wind speed range from 1600.0 to 5400.0 m/s (1.6 to 5.4 m/s). Thus, the internal ventilation in TM has better results than PHP 2000.

Based on Table 31, the TM cases had recorded numerous results with the highest mean of 544.7 l/s, compared to the results in the PHP 2000 cases, which were less than 40.0 l/s. In TM, both cases recorded high air movement for maximum external ventilation ranging from 2160.1 l/s to 5331.5 l/s (2.1 to 5.3 m/s), compared to lower results in PHP 2000.

From the results, TM has achieved the better level of wind speed. Therefore, the results have proved that TM has a better thermal comfort than PHP 2000. Figure 61 shows the days of minimum and maximum internal ventilation for the first floor level in TM, where cross ventilation has functioned properly through its openings.

Figure 62 shows the days of minimum and maximum external ventilation in TM for the tenth floor unit, where the amount of air movement increases compared to first floor unit. The increment of air movement for the tenth floor unit is 36% more than the first floor unit; each floor receives an increase of 3.6% of air movement. As the tenth floor unit receives the maximum level of preferred air movement of 5.4 m/s, the opening areas for the eleventh floor and above should be reduced gradually to maintain the preferred level of air movement.

From the tables and figures discussed, it can be concluded that the longitudinal plan layout that has long external walls receives a higher volume of air; the volume increases as the altitude increases. The placement of the windows and louvers opposite one another in TM cases produces air changes inside the building equal to that of a Malay house.

Carbon Emission and Energy Consumption

Table 32 shows that numerous decreases of energy consumption and carbon emission happened in TM. TM’s carbon emission has reduced by 86%, and its energy consumption decreased by 74.3% compared to PHP 2000 (air conditioned). It can be deduced that an air conditioning system is the biggest culprit for producing high-energy usage in residential buildings in Malaysia. The results proved that the natural ventilation concept used in the building has a tremendous influence on economical and environmental effects. This natural ventilation method can contribute to massive energy savings for the country as well. These results show that TM’s design is practical, environmental friendly and economical.

Researched and written by Mohd Firrdhaus Mohd Sahabuddin; co-founder of 'Air House' and this article was a part of his dissertation which titled 'Traditional Values and Their Adaptation in Social Housing Design: Towards A New Typology and Establishment of ‘Air House’ Standard in Malaysia' for MSc. Advanced Sustainable Design in The University of Edinburgh. Copyright 2012.  

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